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1.
THE CARBONATE FRACTION OF BEACH AND DUNE SANDS 总被引：1，自引：0，他引：1
The sand size carbonate fractions of beach and dune sands from the southeastern U.S. Atlantic coast were investigated from the standpoint of mineralogy, roundness and size distribution. The carbonate fractions of beach-dune sands used in this study range in abundance from less than 1% to over 40% and average about 10%. Calcium carbonate is least abundant in Georgia beaches and increases slightly to the north and greatly to the south. The size distribution of the carbonate fraction is similar to that of the non-carbonate fraction since both have been distributed by the same processes. The variable flat shape of calcareous fragments causes the carbonate fraction to be usually coarser and more poorly sorted than the acid insoluble residues of the samples. No regional relationship between roundness and wave energies was found in sand size materials although field observations indicate high energies strikingly round gravel sized calcareous fragments. There is some tendency for angularity to increase with decreasing grain size in the sand sizes as with quartz grains. The mineralogy of beach sand carbonate fractions is characterized by the almost total absence of high My calcite. Aragonite is the dominant mineral. 相似文献
2.
HOUSTON C. SAUNDERSON 《Sedimentology》1977,24(5):623-638
The Guelph esker (Ontario, Canada) consists of a sinuous, steep-sided and segmented ridge which comprises poorly sorted, matrix-supported sands and gravels. These sands and gravels were probably deposited during the sliding bed stage which has been observed by others in closed-conduit hydraulic experiments. The poor sorting probably resulted from a high concentration of bed-material load in the lower part of a subglacial tunnel, sorting being restricted to that produced by particle collisions. Inclusive graphic standard deviation is characteristically large for the sands and gravels, indicating that virtually all sizes available were in transport. The overall grain size distribution shows a characteristic undulatory shape on arithmetic probability paper, mostly because of selective removal of pebble gravel and granule sizes. This poorly sorted fades is believed to be diagnostic of transport in a subglacial tunnel flowing full of water, and may be used to identify subglacial conditions in other eskers. Deltaic sands and gravels occur downcurrent of the esker and contain a greater diversity of structures; climbing-ripple cross-laminae, parallel laminae and massive structure, deposited in large-scale foresees at the end of a subglacial tunnel. These deltaic sands and gravels grade distally into outwash sands and gravels. 相似文献
3.
Dominique Ngan-Tillard Johan Haan David Laughton Arno Mulder Art Nooy van der Kolff 《Engineering Geology》2009,108(1-2):54-64
Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results. 相似文献
4.
中国北方风沙沉积物气候代用指标对比研究 总被引：2，自引：0，他引：2
在浑善达克沙地和巴丹吉林沙漠各选择近NS走向的大断面采集表层样品,用筛析法对样品进行粒度分析,用Eijkelkamp碳酸钙测定仪测定其碳酸钙含量。两地沙质沉积物的粒度参数对比结果显示,巴丹吉林沙漠沙总体上比浑善达克沙地沙粗,分选性比浑善达克沙地沙好,同时在粒度分布频率曲线上表现出明显的双峰,这应与其地处冬夏季风交替地带、冬季风和夏季风搬运营力上的差别有关。巴丹吉林沙漠和浑善达克沙地沙质沉积物粒度参数上的差别反映了两地不同的风动力条件和下垫面性质。浑善达克沙地的沙粒较细在一定程度上也与该地区较湿润条件下的成土作用有关。气候差异应是导致两地沙质沉积物粒度参数区别的主导因素。碳酸钙测量结果说明,浑善达克沙地的碳酸钙含量明显低于巴丹吉林沙漠。巴丹吉林沙漠沙的碳酸钙含量从北往南呈增加趋势,与该地区年降水量的南北方向变化相一致。从对这两个地区沙质沉积物的碳酸钙含量对比中可以看出,即使在干旱背景下,当多年平均降雨量达到一定临界值时,地表碳酸钙含量将达到一最大值,随后则呈降低趋势 相似文献
5.
BRIAN WILLETTS 《Sedimentology》1983,30(5):669-679
Aeolian transport rates were measured for three sands: a quartz sand (relative density 2.68, sphericity 0.73), a shelly sand (relative density 2.64, sphericity 0.59, carbonate content 67%), and granular aluminium oxide (relative density 3.95, sphericity 0.67). Low sphericity depresses the transport rate, particularly at high wind speeds; high density also does so but the effect is more marked at low transporting wind speeds. The sand of low sphericity undergoes longer saltations than the other materials, but is dislodged less frequently than they are and is transported less freely in a given wind. Of the more spherical materials, the denser was the least effective at extracting energy from the wind for grain transport in the range of our experiments. Both of the more spherical materials showed evidence of a fairly sudden transition of transport behaviour at modest wind speed. It is inferred that this marks the transfer of the function of grain dislodgement from direct wind action to inter-granular collision. The transition did not occur in experiments on the material of lower sphericity. For a given transport rate, wind speed near the bed is highest for the grains of low sphericity (by a considerable margin) and lowest for the more compact quartz grains. Propensity for transport by wind is greatest for the quartz sand, less so for the heavy material and least for the material of low sphericity. 相似文献
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7.
K. N. Murali Krishna K. S. N. Reddy Ch. Ravi Sekhar P. Ganapathi Rao K. Bangaku Naidu 《Journal of the Geological Society of India》2017,89(1):111-111
The study presents the textural characteristics of late Quaternary red sediments of Bhimunipatnam to understand the process of formation of these sediments. The red sediments are classified into (a) yellow sediments (b) reddish brown sediments (c) brick red sediments and (d) light yellow sediments sequence in the vertical litho section. The yellow sediments, rests on the khondalite basement, comprises of medium grained, moderate to poorly sorted and positively skewed. The rounded pebble beds with trough cross bedding indicate high energy turbulent conditions of deposition. The fining upward sequences indicate sediments were deposited under decreasing energy conditions under fluvial regime.The iron bearing minerals like garnets and pyriboles have undergone chemical weathering under high oxidizing environment resulting in addition of silt and clay to the reddish brown and brick red sediments and concretions were formed by carbonate precipitation. These processes caused changes in the mean grain size and sorting nature of these sediments which are originally aeolian in origin. The light yellow sediments were medium to fine grained, well sorted and similar to modern dune sands in terms of textural parameters. These sediments were deposited under low oxidation environmental conditions and acquired yellow colour due to Fe hydroxides. 相似文献
8.
Uppermost sands of the Red Crag at Walton-on-the-Naze (Essex) and elsewhere in East Anglia have been decalcified to iron-stained quartz sands. In contrast, lower sands are only minimally altered and contain aragonitic and calcitic shells. Aragonitic shells are slightly dissolved (chalkified), but calcitic shells are unaffected. Cementation is limited to an addition of iron oxides, now mainly haematite, which also coat carbonate grains. Abundant iron-oxide fines in the upper decalcified sands were liberated from the coatings of shells; shells that have since dissolved. The diagenetic nature of the contact between decalcified upper and unaffected lower sands is evident where it transects cross-bedding. The contact is knife-sharp, even smoothly truncating large shells, and is usually planar and subhorizontal. Shelly sands immediately beneath the boundary contain similar amounts of aragonitic material, as do sands further below. Locally the decalcification boundary has been contorted by cryoturbation, implying that carbonate dissolution was a Pleistocene event. Decalcification probably occurred when the area was affected by permafrost. Lower sands were cemented by ice and protected from dissolution. Upper sands were above the ice table and subject to chemically aggressive waters during summer thaws. Decalcification is believed to have taken place during an episode of climate amelioration when downward retreat of the ice table accompanied replacement of tundra by boreal forest. Highly acidic and podzolic soils developed, beneath which shell-carbonate dissolved. Sharp based decalcified zones in Lowestoft Till and Devensian deposits in other parts of England can also be attributed to dissolution associated with permafrost. 相似文献
9.
混积岩一例--滇东震旦系陡山沱组砂质砂屑白云岩的成因 总被引：11，自引：2，他引：9
滇东震旦系陡山沱组顶部的砂质砂屑白云岩是一例典型的混积岩,即狭义的混合沉积。岩石中的石英砂分选好,圆度和球度高,它们时稀时密地呈“悬浮”状散布在白云石砂屑沉积物中。其产状及结构构造特征表明,它是当时的海滩砂在海进过程中被搬运到海洋中,并与白云石砂屑混合而形成的。 相似文献
10.
Late Miocene fluvial sediment transport from the southern Appalachian Mountains to southern Florida: An example of an old mountain belt sediment production surge 
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下载免费PDF全文 Past geomorphological models assume that erosion of sediments from old mountain belts occurred at a relatively constant rate, based on comparatively uniform isostatic adjustment caused by unloading. Late Miocene strata of the south‐eastern United States provide an example of pulsed tectonism resulting in a surge in siliciclastic sediment production and transport. Regional tectonism (uplift of the southern Appalachian Mountains) and climatic conditions during the Late Miocene resulted in the long‐distance (up to 1000 km) fluvial transport of coarse siliciclastic sediments onto a stable carbonate platform in southern Florida. The sediments are unusual in that they are significantly coarser than marine‐transported sands in southern Florida, with discoidal quartz and quartzite clasts up to 40 mm in diameter locally present, and have relatively high potassium feldspar contents (up to 16% in some sample fractions), whereas feldspar is rare in modern Florida beach sands. It is suggested that previously documented rejuvenation of the southern Appalachian Mountains during the Middle to Late Miocene time, coupled with the Messenian sea‐level low, generated the increased rate of sediment production and necessary hydraulic gradient to allow rapid transport of coarse sediments. Tectonic influence on the river pathway in Florida, as well as in the southern Appalachian Mountains, may have maintained the river on the narrow carbonate platform. The Florida Platform during the Late Miocene must also have had a sufficiently wet climate to cause episodic transport of the coarse sediments. Siliciclastic sediment transport on the Florida Platform during the Late Miocene greatly differed from Pleistocene to modern conditions, which are dominated by the transport of fine‐grained sands by longshore marine processes. 相似文献
11.
Petrology of glacial sand: implications for the origin and mechanical durability of lithic fragments
The petrology of first cycle (unmodified) and second cycle (reworked) sand at the termini of eleven valley glaciers eroding coarse- to fine-grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands. First cycle sands are coarse- to medium-grained, poorly sorted, fine-skewed, non-modal lithic sands with an average composition of Q21F6L73. Grain-size distributions do not vary with composition or source rock types, although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources. By contrast, second cycle sands are medium-grained, poorly sorted, fine- to coarse-skewed arkosic to lithic sands with an average composition of Q19F40L41, and contain fewer lithic fragments than do first cycle sands. We propose that the origin, mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness, and the particular stress field of the transporting medium. As a result of abrasion, glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain-size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock. Upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point-loading during saltation in addition to shear stress. Point-loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness, so the lithic fragments break into smaller monomineralic grains and/or lithic fragments. Lithic fragments of very coarse sand-size are abundant in first cycle sands, thus refuting, at least for glacial sands, the widely held view that grains of this size are deficient in nature. The presence of fewer grains of this size in second cycle sands indicates that very coarse sand-size lithic fragments can survive recycling, but in greatly reduced proportions due to breakage. 相似文献
12.
A. Y. Kwarteng S. M. Al-Hatrushi W. K. Illenberger A. McLachlan 《Arabian Journal of Geosciences》2016,9(9):557
The nature of Al Batinah coast beach sediments in the Sultanate of Oman was investigated by the analysis of grain size and mineralogy. The beach sediments, mostly light-medium gray green, were predominantly fine sands, with the average grain size of all samples about 200 μm. Some of the particles were gravel (2–16 mm), and some were even larger pebble-size particles (16–256 mm). Some mud (sediment <63 μm) was present, mostly in the sub-tidal sediments. The majority of the samples were skewed to the coarse size with coarse tail partly due to the presence of shell fragments. Approximately 50 % of the beach sediments were quartz with different varieties based on shape and size. The second major component of beach sediment was calcium carbonate which varied from 10 to 65 %. The other components in decreasing order consisted of microbreccia, feldspar, pyroxene, igneous rock fragments, biotite flakes, and heavy minerals. The levels of carbonate were lower in NW Al Batinah coast from Harmul to Al Khaburah but were higher in the SE from Al Khaburah to Al Ghubrah. This could be attributed to either lower carbonate production or more sediment input by wadis along the north-western part of Al Batinah coast. The unique and complex nature of these sediments is largely due to the geology of the terrestrial source area in the Hajar Mountains which contains the famous Samail ophiolite complex and the weak sorting along the shoreline in these tide-modified beaches. 相似文献
13.
JAMES R. STEIDTMANN 《Sedimentology》1982,29(6):877-883
It is well known that sediment sorting according to size, shape and density occurs, but the exact mechanisms involved are poorly understood. To assess the effects of size and density, sand-size spheres of two densities were transported and deposited under controlled flume conditions. Observations on the motion of discrete particles show that grains smaller than bed-roughness grains move continuously and have the same transport velocities regardless of density. For grains near and slightly larger than the roughness, movement is intermittent and, for a given size, heavy particles move more slowly than lights. For grains much larger than bed roughness grains, movement is continuous over the rough surface and light and heavy grains have nearly the same transport velocities. Analyses of bulk sediment deposited from plane-bed transport, show that the size and proportion of heavies decreases and that of lights increases with distance transported. For ripple bed transport, however, the size relations between associated light and heavy grains remains essentially unchanged with transport distance and the proportion of light and heavy grains is extremely variable. These results suggest that size-density sorting in plane-bed transport is a function of the transportabilities identified in the discrete grain studies but that sorting in ripple-bed transport is related to deposition on, and recycling through, the bed forms. Application of these findings to the concept of hydraulic equivalence implies that some indication of bed configuration may be necessary for the concept to be useful. 相似文献
14.
Cool-water skeletal carbonate sediments are forming in Spencer Gulf, South Australia, an area of high salinity and moderate tidal range. Four environments can be distinguished: deeper marine areas (10–20 m); shallow subtidal platforms and banks (2–10 m); intertidal and supratidal zones; and coastal springs and lakes fed by saline continental groundwaters. The sediments are predominately bioclastic carbonate sands; muddy sediments occur in protected intertidal environments. The most common grain types are gastropods, bivalves, foraminifera, coralline algae and quartz. Indurated non-skeletal carbonate grains have not been seen. Composition of the sediment varies little between environments, but considerable textural variation results from variation in the stability of the substrate, hydrodynamic conditions, depth of water, period of tidal inundation, supply of terrigenous grains, temperature, and salinity. The Spencer Gulf data suggests that temperature, and particularly minimum temperature, controls the distribution of skeletal and non-skeletal grain associations in high-salinity environments. The textures of the sedimentary facies of Spencer Gulf closely parallel those of equivalent environments in warm-water carbonate provinces. 相似文献
15.
钙质碳酸盐碎屑是热带海滩沉积物的重要组成部分,其物理特性与海滩中的石英颗粒差异明显。对海南岛东部文昌铜鼓角两侧海湾海滩砂样采用除钙和不除钙两种预处理方法,使用Mastersizer 2000激光粒度仪和筛析法进行粒度分析,结果表明:除钙以后粒度频率曲线主体朝细偏,但在粒度频率曲线细尾(4~9)会新增一小峰;去钙前后粒度参数存在明显的线性相关,平均粒径、分选系数和偏态的相关系数依次降低;粒度参数的组合变化以“平均粒径变细、分选系数变好、偏态朝细偏”为主,但仍存在其他的组合变化;在对类似于铜鼓岭周边环境的海滩进行沉积物粒度分析及动力环境研究时,需要了解钙质碎屑含量和颗粒组成。 相似文献
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18.
Geochemical, mineralogical and sedimentological studies on the Taklimakan Desert sands 总被引：7，自引：0，他引：7
Major-element composition, mineral composition and grain-size distribution have been studied for Quaternary aeolian sediments from the Taklimakan Desert, north-western China, together with the variation of chemical and mineralogical compositions of different grain-size fractions. Aeolian sediments from the Taklimakan Desert have higher ratios of feldspar/quartz and calcite/quartz, finer grain size, poorer roundness of quartz and feldspar grains and lower abundances of frosted quartz, than found in aeolian sediments from other deserts such as the Saudi Arabian Desert. In spite of these immature mineralogical and sedimentological features, the aeolian sediments from the Taklimakan Desert show low regional variations in major-element and mineral compositions and are homogenized. These observations confirm that two processes, glacial activity within surrounding mountains and aeolian activity at the Tarim Basin, are important in the homogenization of the Taklimakan Desert sands. Taklimakan Desert sediments are constantly and effectively supplied from basement rocks in the surrounding mountains by glacial erosion. The supplied sediments are further homogenized by aeolian activity in the desert and are partly blown away, serving as the source of Chinese aeolian loess. Compositional differences are observed between loess (mainly 10–40 μm particles) and the <45 μm fraction of the Taklimakan Desert sediments, as well as between loess and whole rock of the Taklimakan Desert sediments. These observations provide constraints for precise modelling of loess formation, and for assessment of the chemical composition of the upper continental crust based on the chemical composition of aeolian loess. 相似文献
19.
P. Poon E. A. C. Liepa D. R. Cohen I. J. Pringle D. A. Burkett 《Australian Journal of Earth Sciences》2020,67(4):575-590
AbstractThere is significant economic interest in the Murray Basin of southeastern Australia as it is proving to be a major heavy mineral sands (HMS) province that will be one of Australia’s major source for production of rutile, zircon and ilmenite. The distribution and provenance of HMS resources in the Murray Basin is poorly understood because of its huge size, limited exploration and the complex depositional, structural and weathering mechanisms in their development. In this paper, we focus on the Copi North and Magic deposits some 130–180?km south of Broken Hill, NSW. The heavy mineral assemblages of the Copi North and Magic deposits are very similar, with the main economic minerals being ilmenite, leucoxene, pseudorutile, rutile and zircon. Intensive fracturing and brecciation are identified in many samples and are inferred to have been initially caused by multi-stage deformational processes associated with metamorphism and then further developed through alluvial and eolian transportation. Both deposits are classified as ‘medium sands, symmetrical, mesokurtic and moderately well-sorted’. The majority of economic minerals are of low to medium sphericity and subrounded, along with abundant polished eolian quartz grains. The Copi North deposit has coarser and more poorly sorted sediments with higher HMS grades and magnetics content than the Magic deposit, reflecting a higher energy depositional environment. The main source for the HMS for the Copi North and Magic deposits is largely ascribed to the Broken Hill Block. Previous studies have shown that the Broken Hill orebody underwent substantial sub-aerial weathering over hundreds of millions of years. In addition, the complex metamorphic events experienced by the Broken Hill Block were capable of forming the broad series of minerals identified within the Copi North and Magic deposits. The HMS were believed to have been transported through paleovalleys near the Mulculca Fault in a southeast direction representing a feeder system into the NW Murray Basin. Both deposits feature a relatively linear geometry (roughly parallel to the strike of the paleoshoreline), with high HMS grades, modest tonnages, and coarser sediments when compared to WIM-style offshore deposits. Compared to other strandline HMS deposits of the Murray Basin, they are smaller in size although have similar high grades of 3.7–6.9% THM and similar proportions of the HMS assemblage of ilmenite, leucoxene, rutile and zircon. Deposits of similar size and grade are likely to occur throughout the northern part of the Murray Basin.
- KEY POINTS
Both the Copi North and Magic deposits contain similar mineral assemblages with the provenance of the heavy minerals ascribed to the Broken Hill Block.
A relatively high energy inshore environment is inferred for the Copi North deposit while a lower energy environment associated with either a foreshore or backshore environment is inferred for the Magic deposit.
Deposits of similar mineralogy, grades and size are likely to occur elsewhere throughout the northern Murray Basin.
20.
石英是地球表面分布最广的矿物之一,抗风化能力较强且性质稳定,是母岩信号的最佳载体。前人研究结果表明石
英的释光（包括光释光OSL 和热释光TL） 灵敏度和母岩以及沉积过程存在一定关系,已初步被应用于沙漠沉积物的判源研
究中。河流与海域沉积物相关研究在国内研究较少,文章拟尝试对中国东部沿海三条重要河流（黄河、长江和浊水溪） 沉
积物中的石英释光性质进行分析,探讨其应用于物源判别的可能性。通过7 个粒级（<4 μm 、4~16 μm 、16~32 μm 、32~
45 μm 、45~63 μm 、63~90 μm 、90~125 μm） 的石英释光灵敏度的对比分析发现,同一河流下游河口沉积物中不同粒级的
石英释光灵敏度差异明显,<4 μm 和>45 μm 粒级的石英110℃TL 峰和OSL 灵敏度较小,4~45 μm 粒级较强;黄河、长江
和浊水溪同粒级沉积物中石英110℃TL 峰和OSL 灵敏度均有明显差异,尤其是63 μm 以下粒级,均表现为长江最大,黄河
次之,浊水溪最小。母岩差异和流域搬运-沉积过程是影响河流沉积物石英释光灵敏度的主要因素。沉积物在长江流域内
的滞留时间长,石英在流域内的辐照-晒退循环次数增多从而使其释光灵敏度增大,同时流域内广泛分布的富含微量元素
的火成岩产出的石英晶体晶格缺陷较多,这两者导致其石英释光灵敏度较大。黄河河口沉积物中石英释光灵敏度继承了其
源区黄土高原的特征。浊水溪是山溪性短途河流,水面坡降大,沉积物可迅速被从源区搬运至河口区,石英接受辐照-晒
退循环次数少,且其源区母岩多以变质岩为主,这可能是其石英释光灵敏度偏小的原因。石英释光灵敏度随粒级的变化,
推测与石英自身发光性质以及河流中沉积物搬运方式的不同有关。泥沙入海后,石英释光灵敏度虽然存在随海域搬运-沉
积过程增大的可能性,但据上述研究来看,其增加幅度可能远小于长江、黄河和浊水溪河流间石英释光灵敏度的差值,因
此可尝试利用细粒级（4~45 μm） 石英释光灵敏度为指标进行黄、东海陆架物源追踪探索。 相似文献